Superconductive copper-containing oxide materials of the formula Ap Bq Cu2 O4±r

ABSTRACT

A superconductive oxide material having an infinite layer structure and having the following formula: 
     
         A.sub.p B.sub.q Cu.sub.2 O.sub.4±r 
    
     wherein A and B are different and each represent an element selected from lanthanoid elements and elements belonging to Groups IA, IIA and IIIA of the Periodic Table, p is between 0.9 and 1.1, q is between 0.9 and 1.1 and r is between 0 and 0.6. The oxide material has a crystal structure belonging to a tetragonal system of P4/mmm and 1-123 having the following lattice parameters: 
     
         3.8Å≦a≦4.0Å 
    
     
         7.6Å≦c≦8.0Å 
    
     or to an orthorhombic system of Pmmm and I-47 having the following lattice parmeters: 
     
         3.8Å≦a≦3.95Å 
    
     
         3.82Å≦b≦4.0Å 
    
     
         7.6Å≦c≦8.0Å.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a copper-containing oxide material useful as asuperconductor or as a parent phase convertible to a superconductor bycarrier doping.

2. Description of the Prior Art

One known oxide having an infinite layer crystal structure is of a (Ca,Sr)CuO₂ system as shown in FIG. 2 which is produced at a super-highpressure of 60,000 atm and a high temperature of 1,000° C. or more (M.Takano et al, Physica C 159, 375(1989)). The illustrated structurecontains one CuO₂ plane and one cation plane in the unit cell. Thecation cite is occupied by a plurality of atoms in the form of a solidsolution. Under ambient pressure, an oxide with such an infinite layerstructure must be prepared at a temperture of 950°-1,150° C. and,therefore, only available is an oxide of the formula Ca₀.84 Sr₀.16 CuO₂(T. Siegrist et al, Nature 334, 231 (1988)). This oxide, which containsa CuO₂ plane commonly included in ceratin superconductors, was expectedto be a mother phase convertible to a superconductive material uponcarrier doping. However, superconductor derived from the oxide has notyet been produced because of difficulties in element substitution.

There are some reports disclosing that superconducting oxides having aninfinite layer structure may be produced at a super-high pressure of20,000-60,000 atm. Namely, the sintering of a composition of Nd_(x)Sr_(l-x) CuO₂ (0.14≦×≦0.16) at 25,000 atm and below 1,000° C. gives asuperconductor having Tc of 40K (M. G. Smith et al, Nature 351, 549(1991)). An infinite layer superconductor of the Ba-Sr-Cu-O system isproduced by a similar high pressure technique (M. Takano et al, PhysicaC 176, 441 (1991)). In these methods, a super-high pressure is used toextend the solid solution limit of the crystallographic phase and,thereby, to control the atoms entering the cation site located betweenthe two CuO₂ planes.

It is reported that cation orderings are important to obtainsuperconductivity of a compound such as (La, Sr)₂ CaCu₂ O₆ (T. Sakuraiet al, Physica C 174, 187 (1991)).

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided an oxidematerial having the following formula:

    A.sub.p B.sub.q Cu.sub.2 O.sub.4±r

wherein A represents an element selected from the group consisting oflanthanoid elements and elements belonging to Groups IA, IIA and IIIA ofthe Periodic Table, B is an element different from element A andselected from the group consisting of lanthanoid elements and elementsbelonging to Groups IA, IIA and IIIA of the Periodic Table, and p, q andr are numbers in the following ranges:

    0.9≦p≦1.1

    0.9≦q≦1.1

    0≦r≦0.6.

In one aspect, the oxide material has a crystal structure which belongsto a tetragonal system of P4/mmm and I-123 and which has the followinglattice parameters:

    3.8Å≦a≦4.0Å

    7.6Å≦c≦8.0Å

the oxide material having an infinite layer structure composed of thefollowing recurring unit:

CuO₂ plane--single layer cation site A(1)-CuO₂ plane--single layercation site A(2),

wherein said cation cites A(1) and A(2) are occupied by elements A andB, respectively. One example of the crystal structure parameters of thisoxide material is shown in Table 1 below.

                  TABLE 1                                                         ______________________________________                                        Structure Parameters                                                                       Position of Atom                                                 Atomic Site    x          y      z                                            ______________________________________                                        A(1)         1a    0          0    0                                          A(2)         1b    0          0    0.5                                        Cu           2h    0.5        0.5  0.25                                       O            4i    0          0.5  0.25                                       ______________________________________                                    

In another aspect, the oxide material has a crystal structure whichbelongs to an orthorhombic system of Pmmm and I-47 and which has thefollowing lattice parameters:

    3.8Å≦a≦3.95Å

    3.82Å≦b≦4.0Å

    7.6Å≦c≦8.0Å

the oxide material having an infinite layer structure composed of thefollowing recurring unit:

CuO₂ plane--single layer cation site A(1)-CuO₂ plane--single layercation site A(2),

wherein the cation cites A(1) and A(2) are occupied by elements A and B,respectively. One example of the crystal structure parameters is givenin Table 2 and the powder X-ray diffraction pattern thereof is shown inFIG. 3.

                  TABLE 2                                                         ______________________________________                                        Structure Parameters                                                                       Position of Atom                                                 Atomic Site    x          y      z                                            ______________________________________                                        A(1)         1a    0          0    0                                          A(2)         1c    0          0    0.5                                        Cu           2t    0.5        0.5  0.25                                       O(1)         2s    0.5        0    0.25                                       O(2)         2r    0          0.5  0.25                                       ______________________________________                                    

Table 3 below shows the critical temperatures and lattice parameters(length of a-axis) of known copper oxide superconductors. As will beseen by comparison of the results shown in Tables 4 and 5, shown inhereinafter, with those shown in Table 3, the lattice parameters of theoxides of the present invention match those of the knownsuperconductors. Therefore, the oxide materials of the present inventionmay be suitably used as an insulating substrate for supporting thereon athin superconducting film. By controlling the lattice parameter, theorientation of the film can be adjusted. Further, since the electricalproperties of the oxide material can be varied at will from an insulatorto a conductor, the oxide material can lend itself to a variety ofutilizations.

                  TABLE 3                                                         ______________________________________                                        Superconducting                                                                            Critical      Lattice                                            Oxide        Temperature (K.)                                                                            Parameter (Å)                                  ______________________________________                                        La.sub.1.85 Sr.sub.0.15 CuO.sub.4                                                          37.5          3.7793                                             Nd.sub.1.4 Ce.sub.0.2 Sr.sub.0.4 CuO.sub.4                                                 28            3.8563                                             Nd.sub.1.85 Ce.sub.0.15 CuO.sub.4                                                          24            3.95                                               YBa.sub.2 Cu.sub.3 O.sub.6.91                                                              91            3.8836                                             YBa.sub.2 Cu.sub.4 O.sub.8                                                                 80            3.869                                              Y2Ba.sub.4 Cu.sub.7 O.sub.14                                                               40            3.851                                              Pb.sub.2 Sr.sub.2 NdCu.sub.3 O.sub.8                                                       70            3.853                                              TlBa.sub.2 CaCu.sub.2 O.sub.7                                                              103           3.8566                                             TiBa.sub.2 Ca.sub.2 Cu.sub.3 O.sub.9                                                       110           3.853                                              Tl.sub.2 Ba.sub.2 CuO.sub.6                                                                70            3.868                                              Bi.sub.2 Sr.sub.2 CuO.sub.6                                                                9             3.796                                              TlBa.sub.2 CaCu.sub.2 O.sub.8                                                              99            3.8558                                             Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.                                                        90            3.829                                              Tl.sub.2 Ba.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10                                               125           3.8503                                             TiBa.sub.2 Ca.sub.2 Cu.sub.3 O.sub.9                                                       110           3.853                                              ______________________________________                                    

Moreover, the oxide material by itself shows superconductivity. Thus, ina further aspect, the present invention provides a superconducting oxidematerial having the following formula: ABCu₂ O₄.4, wherein A and B areas defined above. This oxide has a crystal structure which belongs to atetragonal system of P4/mmm and I-123 and which has the followinglattice parameters:

    a=3.93Å

    c=7.77Å

The oxide material has an infinite layer structure composed of thefollowing recurring unit:

CuO₂ plane--one cation site A(1)-CuO₂ plane-one cation site A(2),

wherein the cation cites A(1) and A(2) are occupied by elements A and B,respectively, and wherein the atomic sites of the infinite layerstructure are as shown in Table 1.

It is, therefore, the prime object of the present invention to provide anovel, copper-containing oxide material having an infinite layerstructure and suitable as a parent phase for forming a superconductor bycarrier doping, as a substrate for forming a superconductor and as asuperconductor.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome apparent from the detailed description of the preferredembodiments of the present invention which follows, when considered inlight of the accompanying drawings in which:

FIG. 1 is a schematic illustration showing the crystal structure of theoxide material according to the present invention;

FIG. 2 is a schematic illustration of the crystal structure of knownoxide material having an infinite layer structure;

FIG. 3 is a simulated X-ray diffraction pattern determined on the basisof the crystal structure parameters obtained from the results of thecrystal structure analysis using transmission electromicroscopy;

FIG. 4 is an X-ray diffraction pattern of BaSrCu₂ O₃.6 obtained inExample 1;

FIG. 5 is a photograph showing an electron diffraction pattern ofBaSrCu₂ O₃.6 taken with the incident electron beam along the c-axis;

FIG. 6 is a photograph showing an electron diffraction pattern ofBaSrCu₂ O₃.6 taken with the incident electron beam along the a-axis;

FIG. 7 is a photograph showing an electron diffraction pattern ofBaSrCu₂ O₃.6 taken with the incident electron beam along the b-axis;

FIG. 8 is a high resolution electronmicrograph showing the crystallattice of BaSrCu₂ O₃.6 in the a-c cross-section;

FIG. 9 is a graph showing temperature-specific resistivitycharacteristics of BaSrCu₂ O₃.6 of the present invention obtained inExample 1;

FIG. 10 is a graph showing temperature-specific resistivitycharacteristics of BaSrCu₂ O₃.8 of the present invention obtained inExample 1;

FIG. 11 is a powder X-ray diffraction pattern of BaSrCu₂ O₄.2 of thepresent invention obtained in Example 2;

FIG. 12 is a graph showing temperature-specific resistivitycharacteristics of BaSrCu₂ O₄.2 of the present invention obtained inExample 2;

FIG. 13 is a powder X-ray diffraction pattern of BaSrCu₂ O₄.6 of thepresent invention obtained in Example 3;

FIG. 14 is a graph showing temperature-specific resistivitycharacteristics of BaSrCu₂ O₄.6 of the present invention obtained inExample 3;

FIG. 15 is a graph showing temperature-magnetic susceptibilitycharacteristics of BaSrCu₂ O₄.4 of the present invention obtained inExample 3;

FIG. 16 is a powder X-ray diffraction pattern of BaSrCu₂ O₃.9 of thepresent invention obtained in Example 4;

FIG. 17 is a graph showing temperature-specific resistivitycharacteristics of BaSrCu₂ O₃.9 of the present invention obtained inExample 4;

FIG. 18 is a powder X-ray diffraction pattern of BaSrCu₂ O₃.7 of thepresent invention obtained in Example 5;

FIG. 19 is a graph showing temperature-specific resistivitycharacteristics of BaSrCu₂ O₃.7 of the present invention obtained inExample 5; and

FIGS. 20-25 are powder X-ray diffraction patterns of comparative oxidematerials obtained in Examples 1-5.

DETAILED DESCRIPTION OF THE PREFERRED Embodiments of the Invention

The following examples will further illustrate the present invention.

Example 1

Powders of BaCO₃, SrCO₃ and CuO were blended with a molar ratio of 1:1:2and ground in ethanol with a ball mill for 10 hours. The mixture waspellitized and calcined in an oxygen stream under various conditions asshown in Tables 4 and 5 involving a temperature of 900°-1,050° C. and aperiod of time of 10-30 hours. It is preferred that the calcined mass berepeatedly (about 2-4 times) subjectedto a treatment involvingpulverization, pelletization and calcination. The resulting calcinedproducts were each encapsulated in a gold tube and subjected to a highpressure treatment to obtain oxide materials of the present inventionand those which do not fall within the scope of the present invention.The treatments were performed at various conditions as shown in Tables 4and 5 involving a temperature of 900°-1,200° C., a pressure of 4 GPa-6GPa and a treatment time of 1-2 hours to obtain oxide samples Nos. 1- 9.The crystallographic phase and lattice parameters of these products areshown in Tables 4 and 5. The above procedures were repeated in the samemanner as described except that the combination of BaCO₃ and SrCO₃ waschanged as shown in Tables 3 and 4 to obtain oxide samples Nos. 11-28.The conditionsof the preparation and the results are shown in Tables 4and 5. The oxide materials of the present invention show either atetragonal system or an orthorhombic system depending upon theconditions under which they are prepared. The lattice parameters varieswith the combination of cations A and B.

                                      TABLE 4                                     __________________________________________________________________________                       High Pressure        Lattice Parameter                     Sam-                                                                             Raw Material                                                                           Calcination                                                                          Treatment            of ABCu.sub.2 O.sub.4 Phase           ple                                                                              Powder   Temp.                                                                             Time                                                                             Temp.                                                                             Press. Crystallographic                                                                        (Å)                               No.                                                                              A   B    (°C.)                                                                      (Hr)                                                                             (°C.)                                                                      (GPa)                                                                             Time                                                                             Phase     a  b  c                               __________________________________________________________________________     1*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                         900 20 1,200                                                                             6   2  BaSrCu.sub.2 O.sub.3.6                                                                  3.92                                                                             3.94                                                                             7.93                             2*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                         1000                                                                              20 1,100                                                                             4   2  BaSrCu.sub.2 O.sub.3.7                                                                  3.92                                                                             3.94                                                                             7.93                             3*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                         1000                                                                              10 1,000                                                                             6   1  BaSrCu.sub.2 O.sub.3.8                                                                  3.92                                                                             3.94                                                                             7.93                             4*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                         950 20 1,000                                                                             4   1  BaSrCu.sub.2 O.sub.3.8                                                                  3.92                                                                             3.94                                                                             7.93                             5*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                         900 30 1,100                                                                             6   1  BaSrCu.sub.2 O.sub.3.7                                                                  3.92                                                                             3.94                                                                             7.93                             6 BaCO.sub.3                                                                        SrCO.sub.3                                                                         900 20    900                                                                            6   1  BaSrCu.sub.2 O.sub.x, SrCO.sub.3                 7 BaCO.sub.3                                                                        SrCO.sub.3                                                                         950 15   950                                                                             6   1  BaSrCu.sub.2 O.sub.x, SrCO.sub.3                 8 BaCO.sub.3                                                                        SrCO.sub.3                                                                         1000                                                                              15   950                                                                             6   1  BaSrCu.sub.2 O.sub.x, SrO.sub.2                  9 BaCO.sub.3                                                                        SrCO.sub.3                                                                         1050                                                                              10 1,000                                                                             4   1  BaCuO.sub.2, SrCuO.sub.2                        10 BaCO.sub.3                                                                        CaCO.sub.3                                                                         950 10 1,200                                                                             6   2  BaCuO.sub.2, Ca.sub.2 CuO.sub.3                 11 BaCO.sub.3                                                                        CaCO.sub.3                                                                         950 30 1,000                                                                             4   2  BaCuO.sub.2, Ca.sub.2 CuO.sub.3                 12 BaCO.sub.3                                                                        CaCO.sub.3                                                                         1000                                                                              30 1,200                                                                             6   1  BaCuO.sub.2, Ca.sub.2 CuO.sub.3                 13 SrCO.sub.3                                                                        CaCO.sub.3                                                                         950 30 1,200                                                                             4   2  (Sr, Ca)CuO.sub.2                               14 SrCO.sub.3                                                                        CaCO.sub.3                                                                         900 20 1,000                                                                             4   1  (Sr, Ca)CuO.sub.2                               15 BaCO.sub.3                                                                        MgCO.sub.3                                                                         1020                                                                              20 1,100                                                                             4   1  BaCuO.sub.2, MgO                                __________________________________________________________________________    *: Oxide material of the present invention                                

                                      TABLE 5                                     __________________________________________________________________________                       High Pressure        Lattice Parameter                     Sam-                                                                             Raw Material                                                                           Calcination                                                                          Treatment            of ABCu.sub.2 O.sub.4                 ple                                                                              Powder   Temp.                                                                             Time                                                                             Temp.                                                                             Press. Crystallographic                                                                        Phase (Å)                         No.                                                                              A   B    (°C.)                                                                      (Hr)                                                                             (°C.)                                                                      (GPa)                                                                             Time                                                                             Phase     a  b  c                               __________________________________________________________________________    16 SrCO.sub.3                                                                        MgCO.sub.3                                                                         1000                                                                              10 1,000                                                                             6   2  SrCuO.sub.2, MgO                                17 CaCO.sub.3                                                                        MgCO.sub.3                                                                         1050                                                                              20 1,000                                                                             4   2  Ca.sub.2 CuO.sub.3, MgO                         18 BaCO.sub.3                                                                        La.sub.2 O.sub.3                                                                    950                                                                              30 1,050                                                                             4   2  (La, Ba)CuO.sub.3-x                             19 La.sub.2 O.sub.3                                                                  SrCO.sub.3                                                                          950                                                                              20 1,000                                                                             4   1  (La, Sr)CuO.sub.2                               20 La.sub.2 O.sub.3                                                                  CaCO.sub.3                                                                         1000                                                                              30 1,100                                                                             4   1  LaCuO.sub.3, CaO                                21*                                                                              BaCO.sub.3                                                                        Nd.sub.2 O.sub.3                                                                    900                                                                              30 1,200                                                                             6   2  BaNdCu.sub.2 O.sub.3.7                                                                  3.95                                                                             3.95                                                                             8.00                            22 SrCO.sub.3                                                                        Nd.sub.2 O.sub.3                                                                   1000                                                                              20 1,150                                                                             6   1  (Nd, Sr)CuO.sub.2                               23 CaCO.sub.3                                                                        Eu.sub.2 O.sub.3                                                                   1000                                                                              30 1,100                                                                             6   1  Nd.sub.2 CuO.sub.4, CaO                         24*                                                                              BaCO.sub.3                                                                        Eu.sub.2 O.sub.3                                                                   1050                                                                              10 1,000                                                                             4   1  BaEuCu.sub.2 O.sub.3.9                                                                  3.82                                                                             3.82                                                                             7.83                            25*                                                                              SrCO.sub.3                                                                        Eu.sub.2 O.sub.3                                                                    950                                                                              10 1,200                                                                             6   1  SrEuCu.sub.2 O.sub.3.9                                                                  3.80                                                                             3.80                                                                             7.80                            26 CaCO.sub.3                                                                        K.sub.2 CO.sub.3                                                                    950                                                                              30 1,000                                                                             4   2  EuCuO.sub.4, CaO                                27 BaCO.sub.3                                                                        Na.sub.2 CO.sub.3                                                                  1000                                                                              30 1,200                                                                             6   1  BaCuO.sub.2, KCuO.sub.2                         28 SrCO.sub.3                                                                        CaCO.sub.3                                                                          950                                                                              30 1,200                                                                             4   2  SrCuO.sub.2, NaCuO.sub.2                        __________________________________________________________________________    *: Oxide material of the present invention                                

The X-ray diffraction pattern of Sample No. 1 (BaSrCu₂ O₃.6) is shown inFIG. 4. The crystallographic phase of this sample was observed with atransmission electron microscope and photographs of the electrondiffraction patterns were taken. FIG. 5 is a photograph of the electrondiffraction pattern of Sample No. 1 with the incident beam along thec-axis. Spots as indicated by the arrow are due to the superstructure of2√2a×2 √2b. FIGS. 6 and 7 are similar photographs of the electrondiffraction pattern with the incident beam along the a- and b-axes,respectively. In FIG. 6, spots (indicated by the arrow) attributedto asuperstructure of 3√2ax3√2b are observed. In FIG. 7, tint spots of thesuperstructure of 2√2ax2√2b as seen in FIG. 5 are seen along the a-axis.

From the results of the electron diffraction patterns, Sample No. 1 isfound to have a crystal structure belonging to an orthorhombic systemhaving lattice parameters of a=3.92, b=3.94 and c=7.93. FIG. 8 shows ahigh resolution electron micrograph of the same sample, with theincident electron beam being perpendicular to the c-axis. From thevariation of contrast, it will be appreciated that there exists anordering along the c-axis in every two unit cells. The period is 7.93 Å.Also found is that the crystal has a two-layered structure in thec-axis. From the results of the electron microscopy, the structureparameters as shown in Table 2 may be determined. FIG. 3 is a simulatedX-ray diffraction patterncalculated on the basis of the structureparameters. It is seen that the simulated fiffraction pattern coincideswith the measured one shown in FIG. 4, indicating that the simulation iscorrect.

Temperature dependence of the specific resistance of Sample No. 1 isshown in FIG. 9, from which it is seen that this oxide material showsmetallic behavior with respect to resistance. This electricalcharacteristics of this material can be changed between an insulator anda metal. FIG. 10 shows temperature-specific resistivity characteristicsof Sample No. 3 (BaSrCu₂ O₃.8). This oxide material shows a behaviorlike a semiconductor with respect to the resistivity. From the resultsshown in FIGS. 9 and 10, it will be appreciated that the characteristicsof the oxide material of this invention can be changed by changing thecontent ofoxygen (the value of r) according to the intended use.

FIGS. 20, 21 and 23 show X-ray diffraction patterns of Sample Nos. 28, 7and 13 (comparative samples), respectively.

Example 2

Powders of BaCO₃, SrCO₃ and CuO were blended with a molar ratio of 1:1:2and ground in ethanol with a ball mill for 10 hours. The mixture waspellitized and calcined in an oxygen stream under various conditions asshown in Table 6 and involving a temperature of 900°-1,000° C. and aperiod of time of 10-30 hours. It is preferred that the calcined mass berepeatedly (about 2-4 times) subjectedto a treatment involvingpulverization, pelletization and calcination. The resulting calcinedproducts were each admixed with KClO₄ (oxydizing agent) in an amountshown in Table 6. The admixture was encapsulated in a gold tube andsubjected to a high pressure treatment to obtain oxide materials of thepresent invention and those which do not fall within the scope of thepresent invention. The treatments were performed at various conditionsas shown in Table 6 and involving a temperature of 900°-1,200° C., apressure of 4 GPa-6 GPa and a treatment time of 1-2 hours to obtainoxide samples Nos. 29-37. The crystallographicphase and latticeparameters of these products are shown in Table 6.

The X-ray diffraction pattern of Sample No. 33 (BaSrCu₂ O₄.2) is shownin FIG. 4. The crystallographic phase of this sample was observed with atransmission electron microscope and the electron diffraction patternswere observed. Sample No. 33 is found to have a crystalstructurebelonging to an orthorhombic system having lattice parametersof a=3.92, b=3.94 and c=7.93. Also found is that the crystal has atwo-layered structure in the c-axis. Temperature dependence of thespecific resistanceof Sample No. 33 is shown in FIG. 12.

FIGS. 22 and 24 show X-ray diffraction patterns of Sample Nos. 36 and 37(comparative samples), respectively.

                                      TABLE 6                                     __________________________________________________________________________                      Amount                                                                             High Pressure         Lattice Parameter                Sam-                                                                             Raw Material                                                                          Calcination                                                                          of   Treatment             of ABCu.sub.2 O.sub.4 Phase      ple                                                                              Powder  Temp.                                                                             Time                                                                             KClO.sub.4                                                                         Temp.                                                                             Press. Crystallo- (Å)                          No.                                                                              A   B   (°C.)                                                                      (Hr)                                                                             (wt %)                                                                             (°C.)                                                                      (GPa)                                                                             Time                                                                             graphic Phase                                                                            a  b  c                          __________________________________________________________________________    29*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                        900 30 0.1  1,200                                                                             6   2  BaSrCu.sub.2 O.sub.3.8                                                                   3.92                                                                             3.94                                                                             7.93                       30*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                        950 20 0.5  1,100                                                                             6   2  BaSrCu.sub.2 O.sub.4.0                                                                   3.92                                                                             3.94                                                                             7.93                       31*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                        920 10 0.5  1,000                                                                             6   1  BaSrCu.sub.2 O.sub.4.4                                                                   3.92                                                                             3.94                                                                             7.93                       32*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                        950 20 0.1  1,000                                                                             4   2  BaSrCu.sub.2 O.sub.3.9                                                                   3.92                                                                             3.94                                                                             7.93                       33*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                        1000                                                                              10 0.3  1,100                                                                             6   1  BaSrCu.sub.2 O.sub.4.2                                                                   3.92                                                                             3.94                                                                             7.93                       34 BaCO.sub.3                                                                        SrCO.sub.3                                                                        900 30 0.05   900                                                                             6   1  BaSrCu.sub.2 O.sub.3.4                      35 BaCO.sub.3                                                                        SrCO.sub.3                                                                        950 15 0.25   950                                                                             6   1  BaSrCu.sub.2 O.sub.x, SrCuO.sub.2           36 BaCO.sub.3                                                                        SrCO.sub.3                                                                        870 15 0.6    950                                                                             6   1  BaSrCu.sub.2 O.sub.x, SrO.sub.2             37 BaCO.sub.3                                                                        SrCO.sub.3                                                                        920 10 0.4  1,000                                                                             4   1  BaCuO.sub.2, SrO.sub.2                      __________________________________________________________________________

Example 3

Powders of BaCO₃, SrCO₃ and CuO were blended with a molar ratio of 1:1:2and ground in ethanol with a ball mill for 10 hours. The mixture waspellitized and calcined in an oxygen stream under various conditions asshown in Table 7 and involving a temperature of 900°-1,000° C. and aperiod of time of 10-30 hours. The resulting calcined products were eachadmixed with KClO₄ (oxydizing agent) in an amount shown in Table 7. Theadmixture was encapsulated in a gold tube and subjected to a highpressure treatment to obtain oxide materials of the present inventionand those which do not fall within the scope of the present invention.The treatments were performed at various conditions as shown in Table 7and involving a temperature of 1,000°-1,200° C., a pressure of 4 GPa-6GPa and a treatment time of 1-2 hours to obtain oxide samples Nos.38-43. The crystallographicphase and lattice parameters of theseproducts are shown in Table 7.

The X-ray diffraction pattern of Sample No. 40 (BaSrCu₂ O₄.6) is shownin FIG. 13. The crystallographic phase of this sample was observed witha transmission electron microscope and the electron diffraction patternswere observed. Sample No. 40 is found to have a crystalstructurebelonging to a tetragonal system having lattice parameters ofa=3.93 and c=7.77. Also found is that the crystal has a two-layeredstructure in the c-axis. Temperature dependence of the specificresistance of Sample No. 40is shown in FIG. 14. Samples Nos. 39 and 40showed Tc of 10K.

FIG. 15 is a graph showing the relationship between temperature andmagnetic susceptibility of the oxide sample No. 38 (BaSrCu₂ O₄.4). Thissample have Tc^(ON) of 40K and Tc^(zero) of 20K and showssuperconductivity.

FIG. 22 shows an X-ray diffraction pattern of Sample No. 41 (comparativesample).

                                      TABLE 7                                     __________________________________________________________________________                      Amount                                                                             High Pressure         Lattice Parameter                Sam-                                                                             Raw Material                                                                          Calcination                                                                          of   Treatment             of ABCu.sub.2 O.sub.4 Phase      ple                                                                              Powder  Temp.                                                                             Time                                                                             KClO.sub.4                                                                         Temp.                                                                             Press. Crystallo- (Å)                          No.                                                                              A   B   (°C.)                                                                      (Hr)                                                                             (wt %)                                                                             (°C.)                                                                      (GPa)                                                                             Time                                                                             graphic Phase                                                                            a  b  c                          __________________________________________________________________________    38*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                        900 30 0.8  1,200                                                                             6   2  BaSrCu.sub.2 O.sub.4.4                                                                   3.93                                                                             3.93                                                                             7.77                       39*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                        950 20 1.5  1,100                                                                             4   2  BaSrCu.sub.2 O.sub.4.6                                                                   3.93                                                                             3.93                                                                             7.77                       40*                                                                              BaCO.sub.3                                                                        SrCO.sub.3                                                                        1020                                                                              10 2.0  1,000                                                                             6   1  BaSrCu.sub.2 O.sub.4.6                                                                   3.93                                                                             3.93                                                                             7.77                       41 BaCO.sub.3                                                                        SrCO.sub.3                                                                        950 20 2.5  1,000                                                                             4   1  BaSrCu.sub.2 O.sub.x, SrO.sub.2             42 BaCO.sub.3                                                                        SrCO.sub.3                                                                        900 30 3.0  1,100                                                                             6   1  BaSrCu.sub.2 O.sub.x, SrO.sub. 2            43 BaCO.sub.3                                                                        SrCO.sub.3                                                                        900 20 0.7  1,200                                                                             6   2  BaSrCu.sub.2 O.sub.4.1                                                                   3.92                                                                             3.94                                                                             7.80                       __________________________________________________________________________

Example 4

Powders of BaO (orBaO₂), SrO₂ (or SrO) and CuO were blended with a molarratio of 1:1:2 and pulverized in a mortar in an inert gas atmsophere.The mixture was encapsulated in a gold tube and subjected to ahighpressure treatment to obtain oxide materials of the present inventionand those which do not fall within the scope of the present invention.Thetreatments were performed at various conditions as shown in Table 8and involving a temperature of 1,000°-1,200° C., a pressure of 4GPa-6GPa and a treatment time of 1-2 hours to obtain oxide samples Nos.44-50. The crystallographic phase and lattice parameters of theseproductsare shown in Table 8.

The X-ray diffraction pattern of Sample No. 46 (BaSrCu₂ O₃.9) is shownin FIG. 16. The crystallographic phase of this sample was observed witha transmission electron microscope and the electron diffraction patternswere observed. Sample No. 46 is found to have a crystalstructurebelonging to an orthorhombic system having lattice parametersof a=3.92, b=3.94 and c=7.93. Also found is that the crystal has atwo-layered structure in the c-axis. Temperature dependence of thespecific resistanceof Sample No. 46 is shown in FIG. 17.

FIG. 25 shows an X-ray diffraction pattern of Sample No. 48 (comparativesample).

                                      TABLE 8                                     __________________________________________________________________________               High Pressure        Lattice Parameter                             Sam-                                                                             Raw Material                                                                          Treatment            of ABCu.sub.2 O.sub.4 Phase                   ple                                                                              Powder  Temp.                                                                             Press. Crystallo-                                                                              (Å)                                       No.                                                                              A   B   (°C.)                                                                      (GPa)                                                                             Time                                                                             graphic Phase                                                                           a  b  c                                       __________________________________________________________________________    44*                                                                              BaO SrO.sub.2                                                                         1,200                                                                             6   2  BaSrCu.sub.2 O.sub.3.7                                                                  3.92                                                                             3.94                                                                             7.93                                    45*                                                                              BaO SrO.sub.2                                                                         1,100                                                                             4   2  BaSrCu.sub.2 O.sub.3.8                                                                  3.92                                                                             3.94                                                                             7.93                                    46*                                                                              BaO SrO.sub.2                                                                         1,000                                                                             6   1  BaSrCu.sub.2 O.sub.3.9                                                                  3.92                                                                             3.94                                                                             7.93                                    47 BaO.sub.2                                                                         SrO.sub.2                                                                         1,000                                                                             4   1  BaO.sub.2, SrCuO.sub.2                                  48 BaO.sub.2                                                                         SrO 1,100                                                                             6   1  BaO.sub.2, SrCuO.sub.2                                  49 BaO SrO 1,000                                                                             6   1  BaSrCu.sub.2 O.sub.x, SrO                               50*                                                                              BaO SrO.sub.2                                                                     8H.sub.2 O                                                                        1,000                                                                             4   1  BaSrCu.sub.2 O.sub.3.9                                                                  3.92                                                                             3.94                                                                             7.93                                    __________________________________________________________________________

Example 5

Powders of Ba(NO₃)₂, Sr(NO₃)₂ and Cu(NO₃)₂ were blended with a molarratio of 1:1:2 and pulverized in a mortar in an inert gas atmsophere.The mixture was evaporated to dryness in an oxygen stream at atemperature of 650°-750° C. for 1-5 hours. The resulting product wasencapsulated in a gold tube and subjected to a high pressure treatmentto obtain oxide materials of the present invention and those which donot fall within the scope of the present invention. The treatments wereperformed at various conditions as shown in Table 9 and involving atemperature of 900°-1,200° C., a pressure of 4 GPa-6 GPa and a treatmenttime of 1-2 hours to obtain oxide samples Nos. 51-56. Thecrystallographic phase and lattice parameters of these productsare shownin Table 9.

The X-ray diffraction pattern of Sample No. 52 (BaSrCu₂ O₃.7) is shownin FIG. 18. The crystallographic phase of this sample was observed witha transmission electron microscope and the electron diffraction patternswere observed. Sample No. 46 is found to have a crystalstructurebelonging to a tetragonal system having lattice parameters ofa=3.93 and c=7.77. Also found is that the crystal has a two-layeredstructure in the c-axis. Temperature dependence of the specificresistance of Sample No. 52is shown in FIG. 19.

FIG. 21 shows an X-ray diffraction pattern of Sample No. 56 (comparativesample).

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrativeand not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all the changes which come within the meaning and rangeof equivalency of the claims are therefore intended to be embracedtherein.

                                      TABLE 9                                     __________________________________________________________________________                  High Pressure     Lattice Parameter                             Sam-                                                                             Raw Material                                                                             Treatment         of ABCu.sub.2 O.sub.4 Phase                   ple                                                                              Powder     Temp.                                                                             Press. Crystallo-                                                                           (Å)                                       No.                                                                              A     B    (°C.)                                                                      (GPa)                                                                             Time                                                                             graphic Phase                                                                        a  b  c                                       __________________________________________________________________________    51*                                                                              Ba(NO.sub.3).sub.2                                                                  Sr(NO.sub.3).sub.2                                                                 1,200                                                                             6   2  BaSrCu.sub.2 O.sub.3.6                                                               3.93                                                                             3.93                                                                             7.77                                    52*                                                                              Ba(NO.sub.3).sub.2                                                                  Sr(NO.sub.3).sub.2                                                                 1,100                                                                             5   2  BaSrCu.sub.2 O.sub.3.7                                                               3.93                                                                             3.93                                                                             7.77                                    53*                                                                              Ba(NO.sub.3).sub.2                                                                  Sr(NO.sub.3).sub.2                                                                 1,000                                                                             6   1  BaSrCu.sub.2 O.sub.3.7                                                               3.93                                                                             3.93                                                                             7.77                                    54 Ba(NO.sub.3).sub.2                                                                  Sr(NO.sub.3).sub.2                                                                 1,000                                                                             3   1  BaCuO.sub.2, SrO                                     55 Ba(NO.sub.3).sub.2                                                                  Sr(NO.sub.3).sub.2                                                                 1,100                                                                             6   1  BaCuO.sub.2, SrO                                     56 Ba(NO.sub.3).sub.2                                                                  Sr(NO.sub.3).sub.2                                                                 1,000                                                                             4   2  BaO.sub.2, SrCuO.sub.2                               __________________________________________________________________________

What is claimed is:
 1. A superconductive oxide material having thefollowing formula:

    A.sub.p B.sub.q Cu.sub.2 O.sub.r±r

wherein A represents an element selected from the group consisting ofelements belonging to Group IIA of the Periodic Table, B is an elementdifferent from element A and selected from the group consisting ofelements belonging to Group IIA of the Periodic Table, and p, q and rare numbers in the following ranges:

    0.9≦p≦1.1

    0.9≦q≦1.1

    0≦r≦0.6

said oxide material having a crystal structure which belongs to atetragonal system of P4/mmm and I-123 and which has the followinglattice parameters:

    3.8Å≦a≦4.0 Å

    7.6Å≦c≦8.0 Å

said oxide material having an infinite layer structure composed of thefollowing recurring unit: CuO₂ plane--single layer cation sitesA(1)-CuO₂ plane--single layer cation sites A(2),wherein said cationsites A(1) are occupied solely by element A and cation sites A(2) areoccupied solely by element B, and wherein the atomic sites of saidinfinite layer structure are as follows:

    ______________________________________                                                 Position of Atoms                                                    Atomic Site                                                                              x            y      z                                              ______________________________________                                        A(1) 1a    0            0      0                                              A(2) 1b    0            0      0.5                                            Cu 2h      0.5          0.5    0.25                                           O 4i       0            0.5    0.25.                                          ______________________________________                                    


2. A superconductive oxide material as claimed in claim 1, whereinelements A and B are Ba and Sr, respectively.
 3. A superconductive oxidematerial as claimed in claim 1 and being a superconductor having thefollowing formula: BaSrCu₂ O₄.4.
 4. A superconductive oxide materialhaving the following formula:

    A.sub.p B.sub.q Cu.sub.2 O.sub.4±r

wherein A represents an element selected from the group consisting ofelements belonging to Group IIA of the Periodic Table, B is an elementdifferent from element A and selected from the group consisting ofelements belonging to Group IIA of the Periodic Table, and p, q and rare numbers in the following ranges:

    0.9≦p≦1.1

    0.9≦q≦1.1

    0≦r≦0.6

said oxide material having a crystal structure which belongs to anorthorhombic system of Pmmm and I-47 and which has the following latticeparameters:

    3.8Å≦a≦3.95Å

    3.82Å≦b≦4.0Å

    7.6Å≦c≦8.0Å

said oxide material having an infinite layer structure composed of thefollowing recurring unit: CuO₂ plane--single layer cation site A(1)-CuO₂plane--single layer cation site A(2),wherein said cation sites A(1) areoccupied solely by element A and cation sites A(2) are occupied solelyby element B, and wherein the atomic sites of said infinite layerstructure are as follows:

    ______________________________________                                                     Position of Atoms                                                Atomic Site    x          y     z                                             ______________________________________                                        A(1)         1a    0          0   0                                           A(2)         1c    0          0   0.5                                         Cu           2t    0.5        0.5 0.25                                        O(1)         2s    0.5        0   0.25                                        O(2)         2r    0          0.5 0.25.                                       ______________________________________                                    


5. An oxide material as claimed in claim 4, wherein elements A and B areBa and Sr, respectively.